Harbison was jointly commissioned by the Pontifical Council for the Promotion of Christian Unity and the Pontifical Council for Inter-religious Dialogue to write a piece for the "Papal Concert of Reconciliation." The event was co-officiated by the Chief Rabbi of Rome, Rav Elio Toaff, the Imam of the Mosque of Rome, Abdulawahab Hussein Gomaa, and Pope John Paul II. Abraham, a six-minute composition for brass and antiphonal choirs, had its world premiere on January 17, 2004, performed by members of the Pittsburgh Symphony Orchestra and a choir made up of members of the Mendelssohn Choir of Pittsburgh, the London Philharmonic Choir, the Krakow Philharmonic Choir, and the Ankara Polyphonic Choir, under the baton of Sir Gilbert Levine.

Harbison was previously the principal guest conductor for Emmanuel Music in Boston; after founding director Craig Smith's untimely death in 2007, Harbison was named Acting Artistic Director.

When asked in 1990 for his "artistic credo" Harbison replied: "to make each piece different from the others, to find clear, fresh large designs, to reinvent traditions."

Koussevitzky Said: Choral Scherzo with Orchestra (2012), for S.A.T.B. choir & orchestra: commissioned by the Boston Symphony Orchestra in Celebration of the 75th Anniversary of the Tanglewood Music Festival